Oxide semiconductor film

ABSTRACT

An oxide semiconductor film includes indium (In), cerium (Ce), zinc (Zn) and oxygen (O) elements, and a molar ratio of the In, Ce, and Zn as In:Ce:Zn is in a range of 2:(0.5 to 2):1. A method for making a oxide semiconductor film includes a step of forming an oxide film on a substrate by using a sputtering method and a sputtering target comprising In 2 Ce x ZnO 4+2x , wherein x=0.5˜2.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims all benefits accruing under 35 U.S.C. §119 fromChina Patent Application No. 201510219946.1, filed on May 4, 2015, inthe China Intellectual Property Office. This application is related tocommonly-assigned applications entitled, Ser. No. 14/749,335 “SPUTTERINGTARGET AND METHOD FOR MAKING THE SAME”, filed Jun. 24, 2015; Ser. No.14/749,345 “THIM FILM TRANSISTOR AND METHOD FOR MAKING THE SAME, THIMFILM TRANSISTOR PANEL AND DISPLAY DEVICE”, filed Jun. 24, 2015.

FIELD

The present disclosure relates to semiconductor manufacture.

BACKGROUND

Display devices should have high resolution, high response speed, lowenergy consumption, high transparency, and flexibility. These qualitiesdepend on performances of thin film transistors (TFTs) used in thedisplay devices. An amorphous silicon TFT has a relatively low carriermobility, which cannot meet the requirements of high resolution andlarge area display. A low temperature poly-silicon (p-Si) TFT can have ahigh mobility. However, a high cost is incurred in creating a large areadisplay device with the p-Si TFT. Recently, an amorphous oxidesemiconductor, indium gallium zinc oxide (InGaZnO₄, or IGZO), has beenproposed. An IGZO based TFT has a high transparency, a low manufacturingtemperature, and a good compatibility with the TFT manufacturingtechnology.

The mobility of the IGZO TFT is between that of the amorphous siliconTFT and the p-Si TFT, thus improvement is still required. An indium zincoxide (IZO) device, with high carrier density and a low stability, isnot a semiconductor but has a higher carrier mobility than that of IGZO.

BRIEF DESCRIPTION OF THE DRAWINGS

Implementations of the present technology will now be described, by wayof example only, with reference to the attached figures.

FIG. 1 is a flowchart of a method for making a sputtering target.

FIG. 2 is a flowchart of a method for making an oxide semiconductorfilm.

FIG. 3 is a schematic view of an embodiment of a TFT.

FIG. 4 shows an X-ray diffraction (XRD) pattern of the oxidesemiconductor film in Example 2-1 post.

FIG. 5 is a diagram showing that electrical properties depend ondifferent oxygen gas flow rates of the oxide semiconductor film inExample 2-1.

FIG. 6 shows a Scanning Electron Microscope (SEM) image of the oxidesemiconductor film in Example 2-1.

FIG. 7 is a diagram showing that different electrical properties dependon different oxygen gas flow rates of the oxide semiconductor film inExample 2-2.

FIG. 8 shows an SEM image of the oxide semiconductor film in Example2-2.

FIG. 9 is a diagram showing the effects of different annealingtemperatures on the electrical properties of the oxide semiconductorfilm in Example 2-3.

FIG. 10 shows an SEM image of the oxide semiconductor film in Example2-3.

DETAILED DESCRIPTION

It will be appreciated that for simplicity and clarity of illustration,where appropriate, reference numerals have been repeated among thedifferent figures to indicate corresponding or analogous elements. Inaddition, numerous specific details are set forth in order to provide athorough understanding of the embodiments described herein. However, itwill be understood by those of ordinary skill in the art that theembodiments described herein can be practiced without these specificdetails. In other instances, methods, procedures, and components havenot been described in detail so as not to obscure the related relevantfeature being described. Also, the description is not to be consideredas limiting the scope of the embodiments described herein. The drawingsare not necessarily to scale and the proportions of certain parts may beexaggerated to better illustrate details and features of the presentdisclosure.

Several definitions that apply throughout this disclosure will now bepresented.

The term “comprise” or “comprising” when utilized, means “include orincluding, but not necessarily limited to”; it specifically indicatesopen-ended inclusion or membership in the so-described combination,group, series, and the like. The term “contact” when utilized, means“direct contact” or “physical contact.”

One embodiment of a sputtering target comprises an indium cerium zincoxide represented by formula In₂Ce_(x)ZnO_(4+2x), wherein x=0.5˜2.

The sputtering target can be obtained by sintering a mixture of indiumoxide (In₂O₃), cerium oxide (CeO₂), and zinc oxide (ZnO). In oneembodiment, the sputtering target is obtained by sintering only themixture of In₂O₃, CeO₂, and ZnO. Impurities may exist in the mixture.Besides In₂O₃, CeO₂, and ZnO, the mixture may only comprise theimpurities. The smaller the amount of the impurities in the mixture thebetter. In one embodiment, the amount of the impurities can be less than10 ppm.

The In₂Ce_(x)ZnO_(4+2x) is a crystal (or crystalline solid). Thesputtering target can also comprise a non crystalline (amorphous) solid.The amorphous solid comprises indium oxide, cerium oxide, and zincoxide. In one embodiment, a weight percentage of the crystallineIn₂Ce_(x)ZnO_(4+2x) in the sputtering target is above 80%.

In one embodiment, the sputtering target only comprises In₂Ce_(x)ZnO₄₊₂,In₂O₃, CeO₂, and ZnO. In another embodiment, the sputtering target onlycomprises In₂Ce_(x)ZnO₄₊₂. Besides In₂Ce_(x)ZnO_(4+2x) (and In₂O₃, CeO₂,and ZnO if have), the sputtering target may only comprise unwanted andtrace amounts of impurities. The smaller the amount of impurities in thesputtering target the better. In one embodiment, the amount ofimpurities in the sputtering target can be less than 10 ppm.

A relative density of the sputtering target can be larger than or equalto 90%. The relative density is a ratio of a real density of thesputtering target to a theoretical density of In₂Ce_(x)ZnO₄₊₂.

A bulk resistance of the sputtering target can be in a range from about10⁻² Ωcm to about 10 Ωcm.

An average surface roughness of the sputtering target can be less thanor equal to 2 microns, and in one embodiment be less than or equal to0.5 microns.

An average flexural strength of the sputtering target can be larger thanor equal to 50 MPa, and in one embodiment be larger than or equal to 55MPa.

FIG. 1 presents a flowchart in accordance with an illustrated exampleembodiment. The embodiment of a method 100 for making the sputteringtarget is provided by way of example, as there are a variety of ways tocarry out the method 100. Each block shown in FIG. 1 represents one ormore processes, methods, or subroutines carried out in the exemplarymethod 100. Additionally, the illustrated order of blocks is by exampleonly and the order of the blocks can be changed. The exemplary method100 can begin at block 101. Depending on the embodiment, additionalsteps can be added, others removed, and the ordering of the steps can bechanged.

At block 101, the In₂O₃ powder, CeO₂ powder, and ZnO powder are mixed toform a mixture. In the mixture, a molar ratio of indium (In), cerium(Ce), and zinc (Zn) as In:Ce:Zn is substantially 2:(0.5 to 2):1.

At block 102, the mixture is sintered at a temperature in a range fromabout 1250° C. to about 1650° C.

In the mixture, the particles of In₂O₃ powder, CeO₂ powder, and ZnOpowder can respectively have an average diameter that is less than orequal to 10 microns. In one embodiment, the average diameter of theparticles of In₂O₃ powder, CeO₂ powder, and ZnO powder can respectivelybe in a range from about 0.5 microns to about 2 microns.

The purity of the In₂O₃ powder, CeO₂ powder, and ZnO powder can be 3N(99.9 mass %) to 5N (99.999%).

A molar ratio of the In₂O₃ powder, CeO₂ powder, and ZnO powder asIn₂O₃:CeO₂:ZnO is substantially 2:(1 to 4):2.

The In₂O₃ powder, CeO₂ powder, and ZnO powder can be mixed in air or ina protective atmosphere (e.g., in argon (Ar) or nitrogen (N₂) gas). Themixing of the In₂O₃ powder, CeO₂ powder, and ZnO powder can furthercomprise steps of: ball milling the In₂O₃ powder, CeO₂ powder, and ZnOpowder together in a liquid medium to form a mixed substance; drying themixed substance to remove the liquid medium to obtain the mixture thatis dry. The liquid medium is not reactive with the In₂O₃ powder, CeO₂powder, and ZnO powder and can be removed from the wet mixed substanceby a drying step, and brings no impurity substance into the mixture. Theliquid medium can be water, ethanol, acetone, or combinations thereof.The ball milling can take place in a ball milling machine. The liquidmedium, In₂O₃ powder, CeO₂ powder, and ZnO powder are introduced intothe ball milling machine. A rotating speed of the ball milling machinecan be about 100 rpm to about 600 rpm. During the ball milling, theIn₂O₃ powder, CeO₂ powder, and ZnO powder mix uniformly, the particlediameters of the powders can decrease, and the specific surface area ofthe particles of the powders can increase. The ball milling can lastuntil the In₂O₃ powder, CeO₂ powder, and ZnO powder are uniformly mixedand the particle diameters of the powders have decreased to the desiredsizes. The mixed substance is taken out from the ball milling machineand dried, for example at about 30° C. to about 60° C., to remove theliquid medium. The mixed substance can be dried in air or a protectiveatmosphere (e.g., Ar gas or N₂ gas). In one embodiment, the mixedsubstance is dried at a high purity (3N to 5N) of protective gas.

The mixture can be sintered in a protective atmosphere (e.g., in argon(Ar) or nitrogen (N₂) gas).

The mixture can be molded or pressed into a desired shape before orduring the sintering step. During the sintering step, the In₂O₃ powder,CeO₂ powder, and ZnO powder react to form the crystalline solidIn₂Ce_(x)ZnO₄₊₂.

A hot pressing method or a hot isostatic pressing (HIP) method can beused to simultaneously mold/press and sinter the mixture. The hotpressing applies a pressure of about 30 MPa to 100 MPa at thetemperature of about 1250° C. to about 1650° C. for about 1 hour toabout 24 hours. The hot isostatic pressing applies a pressure of about100 MPa to 300 MPa at the temperature of about 1250° C. to about 1650°C. for about 1 hour to about 40 hours.

When the sintering step takes place after the molding/pressing step, themolding/pressing step can be processed by using a cold pressing methodor a cold isostatic pressing method. The mixture can be filled into amold and molded/pressed by applying a pressure of about 30 MPa to about300 MPa to form the desired shape. The mixture with the desired shapecan be sintered under normal pressure.

The sputtering target can be obtained directly from the sintering step.In another embodiment, the product of the sintering step can be shapedor polished to form the sputtering target.

One embodiment of an oxide semiconductor film comprises In, Ce, Zn and Oelements, having a molar ratio of In, Ce, and Zn as In:Ce:Zn is 2:(0.5to 2):1. The oxide semiconductor film is an n-type semiconductor havinga carrier density of about 10¹² cm⁻³ to about 10²⁰ cm⁻³, and a carriermobility of about 5.0 cm²V⁻¹s⁻¹ to about 45.0 cm²V⁻¹s⁻¹.

The oxide semiconductor film can be an amorphous solid. In anotherembodiment, the oxide semiconductor film can also comprise crystallinesolid In₂Ce_(x)ZnO₄₊₂.

In one embodiment, unwanted and trace impurities are the only substancein the oxide semiconductor film beyond the elements of In, Ce, Zn and O.The smaller the amount of impurities in the sputtering target thebetter. In one embodiment, the amount of impurities in the oxidesemiconductor film can be less than 10 ppm.

The oxide semiconductor film can have a band gap of about 3.0 eV toabout 3.5 eV.

The oxide semiconductor film can have a visible light transmittance ofabout 60% to about 90%.

The oxide semiconductor film can have a thickness of about 50 nm toabout 1000 nm.

The oxide semiconductor film can have a carrier density of about 10¹³cm⁻³ to about 10¹⁵ cm⁻³.

The oxide semiconductor film can have a carrier mobility of about 12.3cm²V⁻¹s⁻¹ to about 45.0 cm²V⁻¹s⁻¹.

The oxide semiconductor film can be obtained by a sputtering methodusing the sputtering target as described above.

FIG. 2 reveals one embodiment of a method 200 for making the oxidesemiconductor film, comprising a step of sputtering an oxide film on asubstrate by the sputtering method using the sputtering target asdescribed above, as shown in block 201.

The sputtering method can be a DC (direct current) sputter method, an AC(alternating current) sputter method, an RF (radio frequency) sputtermethod, a magnetron sputter method, or a medium frequency magnetronsputter method. The current of the sputtering can be about 0.1 A toabout 2.0 A. The sputtering can take place for about 1 minute to about120 minutes.

The sputtering can be at room temperature or a high temperature (e.g.,smaller than or equal to 400° C.). When the high temperature is used inthe sputtering, the method 200 further comprises a step of preheatingthe substrate. The substrate can be previously heated in vacuum at atemperature of about 50° C. to about 400° C.

A carrier gas is introduced into the sputtering chamber during thesputtering. The carrier gas can be a noble gas, a mixture of a noble gasand oxygen gas, or a mixture of a noble gas and hydrogen gas. In oneembodiment, the noble gas can be Ar gas. For example, the carrier gascan be a mixture of Ar gas and oxygen gas. A flow rate of the oxygen gascan be less than 3 sccm. A purity of the carrier gas can be 3N to 5N.

The pressure in the sputtering chamber during the sputtering can beabout 0.1 Pa to about 2.0 Pa.

The substrate can be an insulating substrate capable of enduring thesputtering temperature. Glass, silicon, or polymer (PET, PI, PE, etc.)can be used as the substrate. When the sputtering is at a relatively lowtemperature (e.g., at room temperature), the choice of the substratematerial is wide.

Before the sputtering, the substrate can be previously cleaned to removeimpurities on the surface of the substrate.

Before the sputtering, the sputtering target can be fixed on a support.An outer surface of the sputtering target can be parallel to the surfaceof the substrate. In another embodiment, an angle can be formed betweenthe outer surface of the sputtering target and the surface of thesubstrate, the angle can be 20° to 85°. A distance between the outersurface of the sputtering target and the surface of the substrate can besmaller than or equal to 8 cm.

The oxide film formed on the surface of the substrate in block 201 canbe directly used as the oxide semiconductor film. In another embodiment,the method can also comprise the annealing step shown in block 202.

In block 202, the oxide film can be annealed in a vacuum, or in an N₂ ornoble gas (e.g., Ar gas) atmosphere. The background vacuum used in theannealing can be about 10⁻³ Pa to about 10 Pa. The annealing temperaturecan be in a range from about 100° C. to about 400° C. A speed oftemperature increase can be in a range from about 1° C./min to about 20°C./min to increase the temperature of the oxide film to the annealingtemperature. The oxide film can be annealed for about 1 hour to about 10hours. The annealing step can slightly increase the crystallization ofthe oxide film to adjust the performance of the oxide semiconductorfilm.

The sputtering target is formed by doping an indium zinc oxide dopedwith Ce to obtain In₂Ce_(x)ZnO_(4+2x), wherein x=0.5˜2. By using thesputtering target, the n-type oxide semiconductor film can be obtained,wherein the molar ratio of In, Ce, and Zn as In:Ce:Zn is 2:(0.5 to 2):1.The carrier density of the n-type oxide semiconductor film can be about10¹² cm⁻³ to about 10²⁰ cm⁻³, and the carrier mobility of the n-typeoxide semiconductor film can be about 5.0 cm²V⁻¹s⁻¹ to about 45.0cm²V⁻¹s⁻¹. The n-type oxide semiconductor film can be used in an n-typeTFT. The amount of Ce in the oxide semiconductor film cannot be toolarge or too small. When x<0.5, the oxide semiconductor film hasproperties similar to those of IZO, which has a relatively lowstability, and thus not proper as a TFT semiconductor. When x>2, theoxide semiconductor film has a relatively low carrier mobility that isnot suitable for high resolution display devices.

One embodiment of a semiconducting device comprises the above describedoxide semiconductor film.

Referring to FIG. 3, one embodiment of a thin film transistor 10comprises an insulating substrate 110, a semiconducting layer 140, asource electrode 151, a drain electrode 152, a gate electrode 120, and ainsulating layer 130. The source electrode 151 and the drain electrode152 are spaced from each other. The semiconducting layer 140 iselectrically connected between the source electrode 151 and the drainelectrode 152. The gate electrode 120 is insulated from thesemiconducting layer 140, the source electrode 151, and the drainelectrode 152 by the insulating layer 130. The semiconducting layer 140can be the above described oxide semiconductor film. The thin filmtransistor 10 can be conventional except the semiconducting layer. Thethin film transistor 10 can be a top gate structure as shown in FIG. 3,or a bottom gate structure.

Example 1 Sputtering Target Example 1-1

209 g of In₂O₃ powder, 260 g of CeO₂ powder and 61 g of ZnO powder witha molar ratio as In₂O₃:CeO₂:ZnO is 1:2:1 and purities of 4N are mixed ina ball milling machine having water as the liquid medium, at a rotatingspeed of about 200 rpm for about 10 hours. After that, the mixedsubstance is dried at a pressure of about 1 atm in an Ar gas atmosphere(5N) for about 1 hour to remove the water. The mixture is hot pressed inAr gas atmosphere at a pressure of about 50 MPa and a temperature ofabout 1350° C. for about 5 hours with a speed of temperature increase ofabout 15° C./min. The obtained sputtering target has a relativedensity >87% and a bulk resistance of 0.75 Ωcm.

Example 1-2

249 g of In₂O₃ powder, 231 g of CeO₂ powder and 73 g of ZnO powder witha molar ratio as In₂O₃:CeO₂:ZnO is 2:3:2 and purities of 4N are mixed ina ball milling machine having ethanol as the liquid medium at a rotatingspeed of about 400 rpm for about 20 hours. After that, the mixedsubstance is dried at a pressure of about 1 atm in an Ar gas atmosphere(5N) for about 1 hour to remove the ethanol. The mixture is placed in amold and cold pressed at a pressure of about 75 MPa for about 60minutes. The molded mixture is sintered at a normal pressure in N₂ gasatmosphere (5N) at a temperature of about 1450° C. for about 8 hourswith a speed of temperature increase of about 10° C./min. The obtainedsputtering target has a relative density >85% and a bulk resistance of0.12 Ωcm.

Example 1-3

209 g of In₂O₃ powder, 260 g of CeO₂ powder and 61 g of ZnO powder witha molar ratio as In₂O₃:CeO₂:ZnO is 1:2:1 and purities of 4N are mixed ina ball milling machine having water as the liquid medium at a rotatingspeed of about 500 rpm for about 10 hours. After that, the mixedsubstance is dried at a pressure of about 1 atm in an Ar gas atmosphere(5N) for about 1 hour to remove the water. The mixture is hotisostatically pressed in Ar gas atmosphere (5N) at a pressure of about100 MPa and a temperature of about 1450° C. for about 20 hours with aspeed of temperature increase of about 10° C./min. The obtainedsputtering target has a relative density >86% and a bulk resistance of0.62 Ωcm.

Example 2 Oxide Semiconductor Film Example 2-1-1

A glass substrate is cleaned and dried by N₂ gas blowing. The glasssubstrate and the sputtering target of Example 1-1 are disposed in asputtering chamber. The surfaces of the sputtering target and thesubstrate are parallel to each other about 8 cm distant. The carriergas, which is Ar gas in this example, is introduced into the sputteringchamber. The Ar gas has a flow rate of about 40 sccm. The pressure inthe sputtering chamber is about 0.7 Pa. The sputtering is at roomtemperature by using a current of about 1.0 A for about 28 minutes toform the oxide semiconductor film with a thickness of about 250 nm.

Example 2-1-2

This example is the same as Example 2-1-1 except that the carrier gas isa combination of Ar gas and O₂ gas. The O₂ gas has a flow rate of about0.25 sccm.

Example 2-1-3

This example is the same as Example 2-1-2 except that the O₂ gas has aflow rate of about 0.5 sccm.

Example 2-1-4

This example is the same as Example 2-1-2 except that the O₂ gas has aflow rate of about 0.75 sccm.

Example 2-1-5

This example is the same as Example 2-1-2 except that the O₂ gas has aflow rate of about 1.0 sccm.

Example 2-1-6

This example is the same as Example 2-1-2 except that the O₂ gas has aflow rate of about 1.5 sccm.

Example 2-1-7

This example is the same as Example 2-1-2 except that the O₂ gas has aflow rate of about 2.0 sccm.

The XRD tests are conducted on the oxide semiconductor films of Examples2-1, and shows that the oxide semiconductor films are amorphous films.One of the XRD patterns is shown in FIG. 4. Hall tests are conducted onthe oxide semiconductor films of Examples 2-1, and reveal that the Hallmobilities of the oxide semiconductor films are about 14 cm²V⁻¹s⁻¹ toabout 25.6 cm²V⁻¹s⁻¹, and the carrier densities of the oxidesemiconductor films are about 10¹³ cm⁻³ to about 10²⁰ cm⁻³. Referring toFIG. 5, the Hall mobilities and carrier densities of the oxidesemiconductor films of Examples 2-1 change with the O₂ gas flow rates.Referring to FIG. 6, the surface morphology of one oxide semiconductorfilm in Examples 2-1 is shown.

Example 2-2-1

A glass substrate is cleaned and dried by N₂ gas blowing. The glasssubstrate and the sputtering target of Example 1-2 are disposed in asputtering chamber. The surfaces of the sputtering target and thesubstrate are parallel to each other at about 8 cm distant. Thesubstrate is preheated to about 250° C. The carrier gas, which is Ar gasin this example, is introduced into the sputtering chamber. The Ar gashas a flow rate of about 40 sccm. The pressure in the sputtering chamberis about 0.7 Pa. The sputtering is at 250° C. by using a current ofabout 1.0 A for about 28 minutes to form the oxide semiconductor filmwith a thickness of about 250 nm.

Example 2-2-2

This example is the same as Example 2-2-1 except that the carrier gas isa combination of Ar gas and O₂ gas. The O₂ gas has a flow rate of about0.5 sccm.

Example 2-2-3

This example is the same as Example 2-2-2 except that the O₂ gas has aflow rate of about 1.0 sccm.

Example 2-2-4

This example is the same as Example 2-2-2 except that the O₂ gas has aflow rate of about 1.5 sccm.

Example 2-2-5

This example is the same as Example 2-2-2 except that the O₂ gas has aflow rate of about 2.0 sccm.

Example 2-2-6

This example is the same as Example 2-2-2 except that the O₂ gas has aflow rate of about 2.5 sccm.

Example 2-2-7

This example is the same as Example 2-2-2 except that the O₂ gas has aflow rate of about 3.0 sccm.

Hall tests are conducted on the oxide semiconductor films of Examples2-2, and reveals that the Hall mobilities of the oxide semiconductorfilms are about 17.8 cm²V⁻¹s⁻¹ to about 45.0 cm²V⁻¹s⁻¹, and the carrierdensities of the oxide semiconductor films are about 10¹⁵ cm⁻³ to about10²⁰ cm⁻³. Referring to FIG. 7, the Hall mobilities and carrierdensities of the oxide semiconductor films of Examples 2-2 change withthe O₂ gas flow rates. Referring to FIG. 8, the surface morphology ofone oxide semiconductor film in Examples 2-2 is shown.

Example 2-3-1

A glass substrate is cleaned and dried by N₂ gas blowing. The glasssubstrate and the sputtering target of Example 1-3 are disposed in asputtering chamber. The surfaces of the sputtering target and thesubstrate are parallel to each other at about 8 cm distant. The carriergas, which is Ar gas in this example, is introduced into the sputteringchamber. The Ar gas has a flow rate of about 40 sccm. The pressure inthe sputtering chamber is about 0.7 Pa. The sputtering is at roomtemperature by using a current of about 1.0 A for about 28 minutes toform the oxide semiconductor film with a thickness of about 250 nm. Theoxide semiconductor film is then annealed an atmospheric pressure of 1Pa for about 1 hour. The annealing temperature is about 150° C.

Example 2-3-2

This example is the same as Example 2-3-1 except that the annealingtemperature is about 200° C.

Example 2-3-3

This example is the same as Example 2-3-1 except that the annealingtemperature is about 250° C.

Example 2-3-4

This example is the same as Example 2-3-1 except that the annealingtemperature is about 300° C.

Example 2-3-5

This example is the same as Example 2-3-1 except that the annealingtemperature is about 350° C.

Hall tests are conducted on the oxide semiconductor films of Examples2-3 before and after the annealing step. Before being annealed, the Hallmobilities of the oxide semiconductor films reach about 15.6 cm²V⁻¹s⁻¹,and the carrier densities of the oxide semiconductor films reach about10²⁰ cm⁻³. After being annealed, the Hall mobilities of the oxidesemiconductor films are about 17.1 cm²V⁻¹s⁻¹ to about 20.6 cm²V⁻¹s⁻¹,and the carrier densities of the oxide semiconductor films are about10¹⁴ cm⁻³ to about 10²⁰ cm⁻³. Referring to FIG. 9, the Hall mobilitiesand carrier densities of the oxide semiconductor films of Examples 2-3change with the annealing temperatures. Referring to FIG. 10, thesurface morphology of one oxide semiconductor film in Examples 2-3 isshown.

Depending on the embodiment, certain of the steps of methods describedmay be removed, others may be added, and the sequence of steps may bealtered. It is also to be understood that the description and the claimsdrawn to a method may comprise some indication in reference to certainsteps. However, the indication used is only to be viewed foridentification purposes and not as a suggestion as to an order for thesteps.

The embodiments shown and described above are only examples. Even thoughnumerous characteristics and advantages of the present technology havebeen set forth in the foregoing description, together with details ofthe structure and function of the present disclosure, the disclosure isillustrative only, and changes may be made in the detail, especially inmatters of shape, size, and arrangement of the parts within theprinciples of the present disclosure, up to and including the fullextent established by the broad general meaning of the terms used in theclaims. It will therefore be appreciated that the embodiments describedabove may be modified within the scope of the claims.

What is claimed is:
 1. An oxide semiconductor film comprises indium(In), cerium (Ce), zinc (Zn) and oxygen (O) elements, and a molar ratioof In, Ce, and Zn as In:Ce:Zn is in a range of 2:(0.5 to 2):1; whereinthe oxide semiconductor film has a carrier density of about 10¹² cm⁻³ toabout 10²⁰ cm⁻³, and a carrier mobility of about 5.0 cm²V⁻¹s⁻¹ to about45.0 cm²V⁻¹s⁻¹.
 2. The oxide semiconductor film of claim 1 being ann-type semiconductor.
 3. The oxide semiconductor film of claim 1 beingan amorphous film.
 4. The oxide semiconductor film of claim 1 having aband gap of about 3.0 eV to about 3.5 eV.
 5. The oxide semiconductorfilm of claim 1 having a carrier density of about 10¹³ cm⁻³ to about10¹⁵ cm⁻³.
 6. The oxide semiconductor film of claim 1 having a visiblelight transmittance of about 60% to about 90%.
 7. The oxidesemiconductor film of claim 1 having about 50 nm to about 1000 nm thick.